Strong-field complexes

The foregoing discussion applies to complexes that are weak-field cases. Spectral analysis for strong-field cases is somewhat different and will not be discussed here. For complete analysis of the spectra of strong-field complexes, see the book by A. B. P. Lever, Inorganic Electronic Spectroscopy, listed in the references at the end of this chapter. 

The complex [Cr(CN)6] is an example of a strong field complex, whereas [Cr(H20)g] is a weak field case. There are N—A electrons to be, attributed corresponding to a sub-configuration of Cr " ". The (lowest... 

A more dramatic example is provided by the complexes of cobalt(III) (sub-configuration 3d ) with NH3 and F . [Co(NH3)6] is a strong field complex (large A value) and its configuration is... 

Strong-field complexes have large A values and absorb high-energy blue, violet, or ultraviolet) radiation. 

There are also some complexes with more than 18 electrons, such as [Ni(H20)6] which possesses 20 electrons ( 1.1.2.1). Some antibond-ing MO must therefore be occupied, which can happen only if they are sufficiently low in energy as is the case in weak-field complexes. Organometallic complexes, characterized by the presence of one or several metal-carbon bonds, are strong-field complexes. It is therefore rare for them to possess more than 18 electrons. 

Organometallic complexes, which contain one or several metal-carbon bonds, are thus strong-field complexes. 

For each of the following metals, write the electronic configuration of the atom and its 2+ ion (a) Mn, (b) Ru, (c) Rh. Draw the crystal-field energy-level diagram for the d orbitals of an octahedral complex, and show the placement of the d electrons for each 2+ km, assuming a strong-field complex. How many impaired electrons are there in each case ... 

The 3d configuration of Cu + forms strong field complexes. In an octahedral complex, one would still expect two electrons with the same spin, since eg orbitals are degenerate. This high spin case has to compete with a low spin case that has another occupation of the orbitals, however. If Cg orbitals are degenerate, we may decide to occupy one of the orbitals with two electrons and leave the other one empty. It turns out that the lowest energy is obtained if the orbital with metal character according to Equation 6.15 (the 3d(z ) orbital) is doubly occupied. 

Answer First determine the number of d electrons in the cation of the complex. In this case the cation is Fe +, which is a d ion. Fe CN)e - with one odd electron is a strong field complex whereas FeFe is a weak field complex,... 

Large energy difference (strong field complex). Electrons enter lower level first, hence there is 1 unpaired electron. 

The octahedral complexes of the first transition series are fairly labile except for those of Cr and Co . The inert complexes of these two cations were among those used by Werner in his historic researches. The octahedral complexes of these cations are inert when they are strong field. Cr(IIl) is a d ion and Co(III) is a d ion. Therefore it appears that when the three lower-energy d orbitals of a strong-field complex are half-filled or filled, a special stability is imparted to the complex. The electron arrangements are shown in Table 22.2. 

Definitions. Define and illustrate the following terms (a) complex ion, (b) ligand, (c) strong-field complex, (d) weak-field complex, (e) geometrical isomerism, (f) kinetic stability, (g) thermodynamic stability. 

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